The New Yale Plunger Device (NYPD)

The New Yale Plunger Device has been commissioned in January  1999, when it performed its first experiment at the YRAST Ball array at Yale. It is the child of Reiner Kruecken, and is based on the design of the Cologne plunger (by Alfred Dewald of the Institute for Nuclear Physics in Cologne, Germany), which has been successfully used with the Gammasphere and EUROBALL arrays.

A standard method to measure lifetimes in the range of about 1ps to several hundred picoseconds is the so-called recoil distance method (RDM). The experimental apparatus used to employ this technique is the so-called plunger, which is a standard apparatus for nuclear gamma-ray spectroscopy, although there are significant variations in the designs used. The basic principle of the plunger apparatus is based on a target and a stopper foil mounted parallel to each other at a variable distance. The nucleus of interest is produced in the target foil and flies a given distance/flight time to the stopper foil. The gamma-ray detectors will observe the original transition energies for the gamma-rays emitted at rest in the stopper foil or Doppler-shifted energies for the gamma-rays emitted in flight. By varying the distance between the two foils the number of transitions observed from nuclei in flight compared to those from nuclei at rest will vary depending on the distances used and the lifetime of the nuclear levels. This variation is then used to extract the lifetimes of the excited nuclear levels.

An important feature of the NYPD is its LabView based control system. This system is used to remote control the plunger from outside the target area. It is used to calibrate the target-to-stopper distances (when measured with a inductive gauge-head) against the capacitance between the two foils. Once beam is on target and the support structure starts expanding due to the heat induced by the beam the distance between the foils is kept constant within <0.1mm by measuring the capacitance several thousand times per second, comparing the average of these measurements to the reference position, and correcting position shifts with a piezoelectric crystal that is expanded or contracted via the remote control system.

The Yale plunger is designed (such as the Cologne plunger shown below) to fit into the Gammasphere array. The first plunger experiment on Gammasphere with the NYPD is scheduled for June 1999.

Anyone who is interested in using the NYPD at Yale with YRAST Ball or with Gammasphere should contact Reiner Krücken.